Scanning line interpolating device

ABSTRACT

A vertical interpolation circuit interpolates an interpolated pixel with pixels located on upper and lower vertical positions, and outputs a vertical interpolated value. An oblique averaging part averages pixels obliquely located with respect to the interpolated pixel on the basis of an oblique edge angle signal, and outputs the result of calculation as an oblique average. An oblique difference absolute value operation part calculates the absolute value of the difference between the values of the pixels obliquely located with respect to the interpolated pixel on the basis of the oblique edge angle signal, and outputs the result of calculation as an oblique difference absolute value. A mixing part outputs the vertical interpolated value, the oblique average or a mixed value thereof as an interpolated pixel value on the basis of the oblique difference absolute value.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a scanning line interpolationequipment for interpolating scanning lines displayed by a video signal.

[0003] 2. Description of the Background Art

[0004] A scanning line interpolation equipment interpolating scanninglines is employed for converting a video signal of an interlacedscanning system to a video signal of a progressive scanning system orincreasing the number of scanning lines in the progressive scanningsystem.

[0005] Such a scanning line interpolation equipment calculates the valueof a pixel (hereinafter referred to as an interpolated pixel) forming ascanning line (hereinafter referred to as an interpolated scanning line)to be created by interpolation on the basis of the values of pixels ofupper and lower scanning lines.

[0006] In this case, it is proposed to calculate the value of theinterpolated pixel with pixels vertically located with respect to theinterpolated pixel in general and to calculate the value of theinterpolated pixel with pixels obliquely located with respect to theinterpolated pixel in an image having an oblique edge or an image havingthin oblique lines. To this end, a correlation determination circuitdetermining a direction having high correlation in an image displayed bya video signal is employed.

[0007] The conventional correlation determination circuit detects thedifference value between two vertical pixels and that between twooblique pixels about the interpolated pixel, for determining the angleof the direction having high correlation on the basis of the differencesvalue. In such a method employing the difference value between twopixels, however, the angle may be falsely detected.

[0008] Therefore, it is proposed to calculate the value of theinterpolated pixel with the vertically located pixels if the differencevalue between two pixels located in the determined direction is greaterthan a threshold while calculating the value of the interpolated pixelwith the oblique pixels if the difference value between the two pixelslocated in the determined direction is less than the threshold.

[0009] In the aforementioned scanning line interpolation equipment,however, the value of the interpolated pixel is so dispersed that nosmooth image can be obtained if the difference value between the twopixels located in the determined direction is approximate to thethreshold.

[0010] Consider an image having an oblique edge as shown in FIG. 13, forexample. It is assumed that the values of two pixels 81 and 82 locatedabove and under an interpolated pixel IN are “0” and “100” respectively,the values of a first pair of oblique pixels 83 and 84 are “0” and “100”respectively, and the values of a second pair of oblique pixels 85 and86 are “80” and “120” respectively. It is also assumed that a thresholdis “40”.

[0011] In this case, the difference value between the two pixels 81 and82 located above and under the interpolated pixel IN is “100”, thatbetween the first pair of oblique pixels 83 and 84 is “100” and thatbetween the second pair of oblique pixels 85 and 86 is “40”, and hencethe direction having high correlation is along a straight lineconnecting the pair of pixels 85 and 86 with each other. In this case,the difference value between the pair of pixels 85 and 86 is not morethan the threshold, and hence the value of the interpolated pixel IN iscalculated with the oblique pair of pixels 85 and 86. For example, theaverage “100” of the pair of pixels 85 and 86 defines the value of theinterpolated pixel IN.

[0012] If the value of the pixel 85 is “75”, however, the differencevalue between the pair of pixels 85 and 86 is greater than thethreshold, and hence the value of the interpolated pixel IN iscalculated with the two pixels 81 and 82 in the vertical direction. Forexample, the average “50” between the values of the two pixels 81 and 82defines the value of the interpolated pixel IN.

[0013] Thus, it follows that the value of the interpolated pixel INvaries by “50” when the value of the pixel 85 varies merely by “5”.Consequently, no smooth image can be obtained.

SUMMARY OF THE INVENTION

[0014] An object of the present invention is to provide a scanning lineinterpolation equipment capable of smoothly interpolating an imagehaving an oblique edge.

[0015] A scanning line interpolation equipment according to an aspect ofthe present invention, interpolating a scanning line by calculating thevalue of a pixel to be interpolated on the basis of an input videosignal, comprises first interpolation means calculating a firstinterpolated value by interpolation employing pixels of upper and lowerscanning lines vertically located with respect to the pixel to beinterpolated, input means inputting a signal indicating the direction ofan image with respect to the pixel to be interpolated, differencecalculation means calculating the difference value between the values ofpixels of upper and lower scanning lines located in the directionindicated by the signal input by the input means with respect to thepixel to be interpolated, second interpolation means calculating asecond interpolated value by interpolation employing the pixels of theupper and lower scanning lines located in the direction indicated by thesignal input by the input means with respect to the pixel to beinterpolated and interpolated value output means outputting the secondinterpolated value calculated by the second interpolation means as thevalue of the pixel to be interpolated when the difference valuecalculated by the difference calculation means is not more than a firstvalue, outputting the first interpolated value calculated by the firstinterpolation means as the value of the pixel to be interpolated whenthe difference value calculated by the difference calculation means isnot less than a second value greater than the first value, andcalculating a third interpolated value by an operation employing thefirst interpolated value calculated by the first interpolation means andthe second interpolated value calculated by the second interpolationmeans and outputting the third interpolated value as the value of thepixel to be interpolated when the difference value calculated by thedifference calculation means is within the range between the first valueand the second value.

[0016] In the scanning line interpolation equipment according to thisaspect of the present invention, the first interpolation meanscalculates the first interpolated value by the interpolation employingthe pixels of the upper and lower scanning lines vertically located withrespect to the pixel to be interpolated. Further, the input means inputsthe signal indicating the direction of the image with respect to thepixel to be interpolated, and the difference calculation meanscalculates the difference value between the values of the pixels of theupper and lower scanning lines located in the direction indicated by theinput signal with respect to the pixel to be interpolated. The secondinterpolation means calculates the second interpolated value by theinterpolation employing the pixels of the upper and lower scanning lineslocated in the direction indicated by the input signal with respect tothe pixel to be interpolated. The interpolated value output meansoutputs the second interpolated value as the value of the pixel to beinterpolated when the difference value is not more than the first value,outputs the first interpolated value as the value of the pixel to beinterpolated when the difference value is in excess of the second valuegreater than the first value, and calculates the third interpolatedvalue by the operation employing the first and second interpolatedvalues and outputs the third interpolated value as the value of thepixel to be interpolated when the difference value is within the rangebetween the first and second values.

[0017] Thus, the value of the pixel to be interpolated is calculated bythe operation employing the first interpolated value calculated with thevertical pixels and the second interpolated value calculated withoblique pixels when the difference value between the pixels obliquelylocated with respect to the pixel to be interpolated is between thefirst and second values, whereby an image having an oblique edge can besmoothly interpolated.

[0018] The interpolated value output means may add the firstinterpolated value calculated by the first interpolation means and thesecond interpolated value calculated by the second interpolation meansto each other in a ratio according to the difference value calculated bythe difference calculation means when the difference value is within therange between the first value and the second value, and outputs theresult of addition as the value of the pixel to be interpolated.

[0019] In this case, the interpolated value output means adds the firstand second interpolated values to each other in the ratio responsive tothe difference value when the difference value is between the first andsecond values, whereby smooth interpolation is enabled.

[0020] The interpolated value output means may add the firstinterpolated value and the second interpolated value to each other sothat the ratio of the first interpolated value calculated by the firstinterpolation means is increased and the ratio of the secondinterpolated value calculated by the second interpolation means isreduced as the difference value calculated by the difference calculationmeans approaches the second value from the first value.

[0021] In this case, the interpolated value output means adds the firstand second interpolated values to each other so that the ratio of thefirst interpolated value is increased and the ratio of the secondinterpolated value is reduced as the difference value approaches thesecond value from the first value, whereby smoother interpolation isenabled.

[0022] The difference calculation means may calculate the differencevalues between the values of a plurality of pixels located in aplurality of directions about the direction indicated by the signalinput by the input means with respect to the pixel to be interpolatedrespectively, and the second interpolation means may calculate aplurality of second interpolated values by interpolation employing theplurality of pixels located in the plurality of directions about thedirection indicated by the signal input by the input means with respectto the pixel to be interpolated respectively, while the scanning lineinterpolation equipment may further comprise minimum value determinationmeans determining the minimum value among the plurality of differencevalues calculated by the difference calculation means and selectionmeans selecting a second interpolated value corresponding to thedifference value determined as the minimum value by the minimum valuedetermination means from the plurality of second interpolated valuescalculated by the second interpolation means and supplying the selectedsecond interpolated value to the interpolated value output means.

[0023] In this case, the scanning line interpolation equipmentcalculates the difference values between the values of the plurality ofpixels located in the plurality of directions about the directionindicated by the input signal with respect to the pixel to beinterpolated respectively, and calculates the plurality of secondinterpolated values respectively by the interpolation employing theplurality of pixels located in the plurality of directions about thedirection indicated by the input signal with respect to the pixel to beinterpolated respectively. The scanning line interpolation equipmentdetermines the minimum value among the plurality of difference valuesfor selecting the second interpolated value corresponding to thedifference value determined as the minimum value from the plurality ofsecond interpolated values and supplies the same to the interpolatedvalue output means.

[0024] Thus, false detection of the angle of the image can be correctedby determining the direction having the highest correlation among theplurality of directions and selecting the second interpolated value inthe direction having the highest correlation from the secondinterpolated values in the plurality of directions.

[0025] The scanning line interpolation equipment may further comprisedetection means detecting the values of pixels vertically located aboveand under the pixel to be interpolated respectively and intermediatevalue determination means determining whether or not the secondinterpolated value calculated by the second interpolation means isbetween the values detected by the detection means, and the interpolatedvalue output means may output the first interpolated value calculated bythe first interpolation means as the value of the pixel to beinterpolated regardless of the difference value calculated by thedifference calculation means when the intermediate value determinationmeans determines that the second interpolated value is not between thevalues detected by the detection means.

[0026] In this case, the scanning line interpolation equipment detectsthe values of the pixels vertically located above and under the pixel tobe interpolated respectively, and determines whether or not the secondinterpolated value is between the detected values. When determining thatthe second interpolated value is not between the detected values, thescanning line interpolation equipment outputs the first interpolatedvalue as the value of the pixel to be interpolated regardless of theoblique difference.

[0027] Thus, the scanning line interpolation equipment can be preventedfrom calculating the value of the pixel to be interpolated with pixelsof a false direction when falsely detecting the angle of the image, byemploying not the second interpolated value but the first interpolatedvalue if the second interpolated value is not between the pixels locatedabove and under the pixel to be interpolated.

[0028] The scanning line interpolation equipment may further comprisevertical difference operation means calculating the difference valuebetween pixels vertically located above and under the pixel to beinterpolated, and the interpolated value output means may output thefirst interpolated value calculated by the first interpolation meansregardless of the difference value calculated by the differencecalculation means when the difference value calculated by the verticaldifference operation means is less than a predetermined value.

[0029] In this case, the scanning line interpolation equipmentcalculates the difference value between the pixels vertically locatedabove and under the pixel to be interpolated, and outputs the firstinterpolated value as the value of the pixel to be interpolatedregardless of the oblique difference value when the vertical differencevalue is less than the predetermined value.

[0030] Thus, deterioration of picture quality resulting from falsedetection of the angle of the image can be prevented by employing notthe second interpolated value but the first interpolated value when thevertical difference value is less than the predetermined value.

[0031] The second interpolation means may average the pixels of theupper and lower scanning lines located in the direction indicated by thesignal input by the input means with respect to the pixel to beinterpolated as the second interpolated value.

[0032] In this case, the second interpolated value is defined by theaverage of the values of the pixels obliquely located with respect tothe pixel to be interpolated.

[0033] The first value may be zero, and the second value may be a presetthreshold.

[0034] In this case, the scanning line interpolation equipment outputsthe second interpolated value as the value of the pixel to beinterpolated when the difference value is zero, outputs the firstinterpolated value as the value of the pixel to be interpolated when thedifference value is in excess of the threshold, and outputs the thirdinterpolated value calculated by the operation employing the first andsecond interpolated values as the value of the pixel to be interpolatedwhen the difference value is within the range between zero and thethreshold.

[0035] The scanning line interpolation equipment may further compriseimage angle detection means detecting an image angle related to thepixel to be interpolated on the basis of the input video signal andsupplying the signal indicating the direction of the image to the inputmeans, and the image angle detection means may include binarized patterngeneration means binarizing the input video signal in a predetermineddetection area including a plurality of scanning lines and the pixel tobe interpolated and generating a binarized pattern, reference patterngeneration means generating a binary image having a plurality ofdirections as a plurality of reference patterns and comparison meanscomparing the binarized pattern generated by the binarized patterngeneration means with each of the plurality of reference patternsgenerated by the reference pattern generation means and detecting theimage angle related to the pixel to be interpolated on the basis of theresult of comparison.

[0036] In the image angle detection means, the binarized patterngeneration means binarizes the input video signal in the predetermineddetection area and generates the binarized pattern. The referencepattern generation means generates the binary image having the pluralityof directions as the plurality of reference patterns. The comparisonmeans compares the binarized pattern with each of the plurality ofreference patterns, and detects the image angle related to the pixel tobe interpolated on the basis of the result of comparison.

[0037] In this case, the scanning line interpolation equipment cansuppress false detection as compared with a case of employing thedifference value between two pixels due to comparison of two-dimensionalpatterns, whereby the angle of the image having an oblique edge can becorrectly detected.

[0038] When employing two-dimensional reference patterns, detectedangles are not restricted to the angle of a straight line connectingpixels located on point-symmetrical positions about the pixel to beinterpolated but angles therebetween can also be detected. Therefore,the angles can be detected at smaller intervals without increasing thecircuit scale.

[0039] The scanning line interpolation equipment may further compriseimage angle detection means detecting an image angle related to thepixel to be interpolated on the basis of the input video signal andsupplying the signal indicating the direction of the image to the inputmeans, and the image angle detection means may include maximal/minimalpattern generation means generating a maximal/minimal pattern indicatingthe position of the maximal point or the minimal point of horizontalluminance distribution every scanning line in a predetermined detectionarea including a plurality of scanning lines and the pixel to beinterpolated in the input video signal, reference pattern generationmeans generating a plurality of reference patterns indicating thepositions of the maximal points or the minimal points of horizontalluminance distribution every scanning line in the detection area andcomparison means comparing the maximal/minimal pattern generated by themaximal/minimal pattern generation means with each of the plurality ofreference patterns generated by the reference pattern generation meansand detecting the image angle related to the pixel to be interpolated onthe basis of the result of comparison.

[0040] In the image angle detection means, the maximal/minimal patterngeneration means generates the maximal/minimal pattern indicating theposition of the maximal point or the minimal point of the horizontalluminance distribution every scanning line in the predetermineddetection area in the input video signal. Further, the reference patterngeneration means generates the plurality of reference patternsindicating the maximal points or the minimal points of the horizontalluminance distribution every scanning line in the detection area. Thecomparison means compares the maximal/minimal pattern with each of theplurality of reference patterns, and detects the image angle related tothe pixel to be interpolated on the basis of the result of comparison.

[0041] In this case, false detection is suppressed as compared with thecase of employing the difference value between two pixels due tocomparison of two-dimensional patterns, whereby the angle of an imagehaving thin oblique lines can be correctly detected.

[0042] When employing two-dimensional reference patterns, detectedangles are not restricted to the angle of a straight line connectingpixels located on point-symmetrical positions about the pixel to beinterpolated but angles therebetween can also be detected. Therefore,the angles can be detected at smaller intervals without increasing thecircuit scale.

[0043] A scanning line interpolation equipment according to anotheraspect of the present invention, interpolating a scanning line bycalculating the value of a pixel to be interpolated on the basis of aninput video signal, comprises a first interpolation device thatcalculates a first interpolated value by interpolation employing pixelsof upper and lower scanning lines vertically located with respect to thepixel to be interpolated, an input terminal that receives a signalindicating the direction of an image with respect to the pixel to beinterpolated, a difference calculation device that calculates thedifference value between the values of pixels of upper and lowerscanning lines located in the direction indicated by the signal receivedin the input terminal with respect to the pixel to be interpolated, asecond interpolation device that calculates a second interpolated valueby interpolation employing the pixels of the upper and lower scanninglines located in the direction indicated by the signal received in theinput terminal with respect to the pixel to be interpolated and aninterpolated value output device that outputs the second interpolatedvalue calculated by the second interpolation device as the value of thepixel to be interpolated when the difference value calculated by thedifference calculation device is not more than a first value, outputsthe first interpolated value calculated by the first interpolationdevice as the value of the pixel to be interpolated when the differencevalue calculated by the difference calculation device is not less than asecond value greater than the first value, and calculates a thirdinterpolated value by an operation employing the first interpolatedvalue calculated by the first interpolation device and the secondinterpolated value calculated by the second interpolation device andoutputs the third interpolated value as the value of the pixel to beinterpolated when the difference value calculated by the differencecalculation device is within the range between the first value and thesecond value.

[0044] In the scanning line interpolation equipment according to thisaspect of the present invention, the first interpolation devicecalculates the first interpolated value by the interpolation employingthe pixels of the upper and lower scanning lines vertically located withrespect to the pixel to be interpolated. The signal indicating thedirection of the image with respect to the pixel to be interpolated isinput in the input terminal, and the difference calculation devicecalculates the difference value between the values of the pixels of theupper and lower scanning lines located in the direction indicated by theinput signal with respect to the pixel to be interpolated. Further, thesecond interpolation device calculates the second interpolated value bythe interpolation employing the pixels of the upper and lower scanninglines located in the direction indicated by the input signal withrespect to the pixel to be interpolated. The interpolated value outputdevice outputs the second interpolated value as the value of the pixelto be interpolated when the difference value is not more than the firstvalue, outputs the first interpolated value as the value of the pixel tobe interpolated when the difference value is not less than the secondvalue greater than the first value, and calculates the thirdinterpolated value by the operation employing the first and secondinterpolated values and outputs the same as the value of the pixel to beinterpolated when the difference value is within the range between thefirst and second values.

[0045] Thus, the scanning line interpolation equipment calculates thevalue of the pixel to be interpolated by the operation employing thefirst interpolated value calculated with the vertical pixels and thesecond interpolated value calculated with oblique pixels when thedifference value between the pixels obliquely located with respect tothe pixel to be interpolated is between the first and second values,whereby an image having an oblique edge can be smoothly interpolated.

[0046] The interpolated value output device may add the firstinterpolated value calculated by the first interpolation device and thesecond interpolated value calculated by the second interpolation deviceto each other in a ratio according to the difference value calculated bythe difference calculation device when the difference value is withinthe range between the first value and the second value, and outputs theresult of addition as the value of the pixel to be interpolated.

[0047] In this case, the scanning line interpolation equipment adds thefirst and second interpolated values to each other in the ratioresponsive to the difference value when the difference value is betweenthe first and second values, whereby smooth interpolation is enabled.

[0048] The interpolated value output device may add the firstinterpolated value and the second interpolated value to each other sothat the ratio of the first interpolated value calculated by the firstinterpolation device is increased and the ratio of the secondinterpolated value calculated by the second interpolation device isreduced as the difference value calculated by the difference calculationdevice approaches the second value from the first value.

[0049] In this case, the interpolated value output device adds the firstand second interpolated values to each other so that the ratio of thefirst interpolated value is increased and the ratio of the secondinterpolated value is reduced as the difference value approaches thesecond value from the first value, whereby smoother interpolation isenabled.

[0050] The difference calculation device may calculate the differencevalues between the values of a plurality of pixels located in aplurality of directions about the direction indicated by the signalreceived in the input terminal with respect to the pixel to beinterpolated respectively and the second interpolation device maycalculate a plurality of second interpolated values by interpolationemploying the plurality of pixels located in the plurality of directionsabout the direction indicated by the signal received in the inputterminal with respect to the pixel to be interpolated respectively,while the scanning line interpolation equipment may further comprise aminimum value determination device that determines the minimum valueamong the plurality of difference values calculated by the differencecalculation device and a selection device that selectes a secondinterpolated value corresponding to the difference value determined asthe minimum value by the minimum value determination device from theplurality of second interpolated values calculated by the secondinterpolation device and supplies the selected second interpolated valueto the interpolated value output device.

[0051] In this case, the scanning line interpolation equipmentcalculates the difference values between the plurality of pixels locatedin the plurality of directions about the direction indicated by theinput signal with respect to the pixel to be interpolated respectively,and calculates the plurality of second interpolated values respectivelyby the interpolation employing the plurality of pixels located in theplurality of directions about the direction indicated by the inputsignal with respect to the pixel to be interpolated respectively. Thescanning line interpolation equipment determines the minimum value amongthe plurality of difference values, for selecting the secondinterpolated value corresponding to the difference value determined asthe minimum value from the plurality of second interpolated values andsupplying the same to the interpolated value output device.

[0052] Thus, false detection of the angle of the image can be correctedby determining the direction having the highest correlation among theplurality of directions and selecting the second interpolated value inthe direction having the highest correlation from the secondinterpolated values of the plurality of directions.

[0053] The scanning line interpolation equipment may further comprise adetection device that detects the values of pixels vertically locatedabove and under the pixel to be interpolated respectively and anintermediate value determination device that determines whether or notthe second interpolated value calculated by the second interpolationdevice is between the values detected by the detection device, and theinterpolated value output device may output the first interpolated valuecalculated by the first interpolation device as the value of the pixelto be interpolated regardless of the difference value calculated by thedifference calculation device when the intermediate value determinationdevice determines that the second interpolated value is not between thevalues detected by the detection device.

[0054] In this case, the scanning line interpolation equipment detectsthe values of the pixels vertically located above and under the pixel tobe interpolated respectively and determines whether or not the secondinterpolated value is between the detected values. When determining thatthe second interpolated value is not between the detected values, thescanning line interpolation equipment outputs the first interpolatedvalue as the value of the pixel to be detected regardless of the obliquedifference value.

[0055] Thus, the scanning line interpolation equipment can be preventedfrom calculating the value of the pixel to be interpolated with pixelsof a false direction when falsely detecting the angle of the image, byemploying not the second interpolated value but the first interpolatedvalue if the second interpolated value is not between the pixels locatedabove and under the pixel to be interpolated.

[0056] The scanning line interpolation equipment may further comprise avertical difference operation device that calculates the differencevalue between pixels vertically located above and under the pixel to beinterpolated, and the interpolated value output device may output thefirst interpolated value calculated by the first interpolation deviceregardless of the difference value calculated by the differencecalculation device when the difference value calculated by the verticaldifference operation device is less than a predetermined value.

[0057] In this case, the scanning line interpolation equipmentcalculates the difference value between the pixels vertically locatedabove and under the pixel to be interpolated, and outputs the firstinterpolated value as the value of the pixel to be interpolatedregardless of the oblique difference value when the vertical differencevalue is less than the predetermined value.

[0058] Thus, picture quality can be prevented from deteriorationresulting from false detection of the angle of the image by employingnot the second interpolated value but the first interpolated value whenthe vertical difference value is smaller than the predetermined value.

[0059] The second interpolation device may average the pixels of theupper and lower scanning lines located in the direction indicated by thesignal received in the input terminal with respect to the pixel to beinterpolated as the second interpolated value.

[0060] In this case, the second interpolated value is defined by theaverage of the values of pixels obliquely located with respect to thepixel to be interpolated.

[0061] The first value may be zero, and the second value may be a presetthreshold.

[0062] In this case, the scanning line interpolation equipment outputsthe second interpolated value as the value of the pixel to beinterpolated when the difference value is zero, outputs the firstinterpolated value as the value of the pixel to be interpolated when thedifference value is in excess of the threshold, and outputs the thirdinterpolated value calculated by-the operation employing the first andsecond interpolated values as the value of the pixel to be interpolatedwhen the difference value is within the range between zero and thethreshold.

[0063] The scanning line interpolation equipment may further comprise animage angle detection device that detects an image angle related to thepixel to be interpolated on the basis of the input video signal andsupplies the signal indicating the direction of the image to the inputterminal, and the image angle detection device may include a binarizedpattern generation device that binarizes the input video signal in apredetermined detection area including a plurality of scanning lines andthe pixel to be interpolated and generates a binarized pattern, areference pattern generation device that generates a binary image havinga plurality of directions as a plurality of reference patterns and acomparison device that compares the binarized pattern generated by thebinarized pattern generation device with each of the plurality ofreference patterns generated by the reference pattern generation deviceand detects the image angle related to the pixel to be interpolated onthe basis of the result of comparison.

[0064] In the image angle detection device, the binarized patterngeneration device binarizes the input video signal in the predetermineddetection area and generates the binarized pattern. The referencepattern generation device generates the binarized image having theplurality of directions as the plurality reference patterns. Thecomparison device compares the binarized pattern with each of theplurality of reference patterns and detects the image angle related tothe pixel to be interpolated on the basis of the result of comparison.

[0065] In this case, false detection is suppressed as compared with acase of employing the difference value between two pixels due tocomparison of two-dimensional patterns, whereby the angle of an imagehaving an oblique edge can be correctly detected.

[0066] When employing two-dimensional reference patterns, detectedangles are not restricted to the angle of a straight line connectingpixels located on point-symmetrical positions about the pixel to beinterpolated but angles therebetween can also be detected. Therefore,the angles can be detected at smaller intervals without increasing thecircuit scale.

[0067] The scanning line interpolation equipment may further comprise animage angle detection device that detects an image angle related to thepixel to be interpolated on the basis of the input video signal andsupplies the signal indicating the direction of the image to the inputterminal, and the image angle detection device may include amaximal/minimal pattern generation device that generates amaximal/minimal pattern indicating the position of the maximal point orthe minimal point of horizontal luminance distribution every scanningline in a predetermined detection area including a plurality of scanninglines and the pixel to be interpolated in the input video signal, areference pattern generation device that generates a plurality ofreference patterns indicating the positions of the maximal points or theminimal points of horizontal luminance distribution every scanning linein the detection area and a comparison device compares themaximal/minimal pattern generated by the maximal/minimal patterngeneration device with each of the plurality of reference patternsgenerated by the reference pattern generation device and detects theimage angle related to the pixel to be interpolated on the basis of theresult of comparison.

[0068] In the image angle detection device, the maximal/minimal patterngeneration device generates the maximal/minimal pattern indicating theposition of the maximal point or the minimal point of the horizontalluminance distribution every scanning line in the predetermineddetection area in the input video signal. The reference patterngeneration device generates the plurality of reference patternsindicating the positions of the maximal points or the minimal points ofthe horizontal luminance distribution every scanning line in thedetection area. The comparison device compares the maximal/minimalpattern with each of the plurality of reference patterns, and detectsthe image angle related to the pixel to be interpolated on the basis ofthe result of comparison.

[0069] In this case, false detection is suppressed as compared with acase of employing the difference value between two pixels due tocomparison of two-dimensional patterns, and the angle of an image havingthin oblique lines can be correctly detected.

[0070] When employing two-dimensional reference patterns, detectedangles are not restricted to the angle of a straight line connectingpixels located on point-symmetrical positions about the pixel to beinterpolated but angles therebetween can also be detected. Therefore,the angles can be detected at smaller intervals without increasing thecircuit scale.

[0071] The foregoing and other objects, features, aspects and advantagesof the present invention will become more apparent from the followingdetailed description of the present invention when taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0072]FIG. 1 is a block diagram showing the structure of a scanning lineinterpolation equipment according to a first embodiment of the presentinvention;

[0073]FIG. 2 is a model diagram for illustrating the relation betweenthe angle of an image and pixels employed for interpolation;

[0074]FIG. 3 is a model diagram for illustrating operations of a mixingpart shown in FIG. 1;

[0075]FIG. 4 is a model diagram showing the relation between an obliquedifference absolute value and coefficients of an oblique average and avertical interpolated value;

[0076]FIG. 5 is a block diagram showing the structure of a scanning lineinterpolation equipment according to a second embodiment of the presentinvention;

[0077]FIG. 6 is a model diagram for illustrating oblique interpolationby an oblique averaging part and an oblique difference absolute valueoperation part of the scanning line interpolation equipment shown inFIG. 5;

[0078]FIG. 7 is a block diagram showing an exemplary structure of animage angle detector outputting an angle signal;

[0079]FIG. 8 illustrates exemplary binarized patterns output from abinarization part shown in FIG. 7;

[0080] FIGS. 9(a) to 9(e) are model diagrams showing exemplary referencepatterns generated from a reference pattern generation part shown inFIG. 7;

[0081]FIG. 10 is a block diagram showing another exemplary structure ofthe image angle detector outputting the angle signal;

[0082]FIG. 11 is a model diagram showing an exemplary maximal/minimalpattern output from an upper line maximal/minimal detection part and alower line maximal/minimal detection part shown in FIG. 10;

[0083] FIGS. 12(a) and 12(b) are model diagrams showing exemplaryreference patterns generated by a reference pattern generation partshown in FIG. 11; and

[0084]FIG. 13 is a model diagram for illustrating interpolation in aconventional scanning line interpolation equipment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0085] (1) First Embodiment

[0086]FIG. 1 is a block diagram showing the structure of a scanning lineinterpolation equipment according to a first embodiment of the presentinvention.

[0087] The scanning line interpolation equipment shown in FIG. 1includes a line memory 1, a vertical interpolation circuit 2, an obliqueaveraging part 3, an oblique difference absolute value operation part 4and a mixing part 5.

[0088] A video signal VD1 is input in the line memory 1, the verticalinterpolation circuit 2, the oblique averaging part 3 and the obliquedifference absolute value operation part 4.

[0089] An angle signal AN is input in the oblique averaging part 3 andthe oblique difference absolute value operation part 4 through an inputterminal 6. An image angle detector described later supplies the anglesignal AN indicating the angle of an oblique image such as an imagehaving an oblique edge or an image having thin oblique lines.

[0090] The line memory 1 delays the input video signal VD1 by one line(one scanning line) and outputs a video signal VD2. The video signal VD2output from the line memory 1 is supplied to the vertical interpolationcircuit 2, the oblique averaging part 3 and the oblique differenceabsolute value operation part 4.

[0091] In this embodiment, it is assumed that the video signals VD1 andVD2 have luminance of 256 gradations. In other words, the minimum andmaximum values of the luminance of the video signals VD1 and VD2 are “0”and “255” respectively.

[0092] The vertical interpolation circuit 2 performs interpolation(hereinafter referred to as vertical interpolation) on an interpolatedpixel (a pixel to be created by interpolation) with pixels verticallylocated above and under the interpolated pixel on the basis of the inputvideo signal VD1 and the video signal VD2 output from the line memory 1,and outputs a vertical interpolated value ID. For example, the verticalinterpolation circuit 2 averages the values of the pixels verticallylocated above and under the interpolated pixel as the verticalinterpolated value ID. A well-known interpolation circuit can beemployed as the vertical interpolation circuit 2. For example, thevertical interpolation circuit 2 may be formed by an interpolationcircuit employing a median filter selecting an intermediate value fromthe values of a plurality of pixels and outputting the same.

[0093] The oblique averaging part 3 averages the values of pixels ofupper and lower scanning lines obliquely located with respect to theinterpolated pixel on the basis of the input video signal VD1, the videosignal VD2 output from the line memory 1 and the angle signal AN, andoutputs the result of this averaging as an oblique average AD. Thiscalculation of the oblique average AD performed by the oblique averagingpart 3 is referred to as oblique interpolation.

[0094] The oblique difference absolute value operation part 4 calculatesthe absolute value of the difference between the values of pixelsobliquely located with respect to the interpolated pixel on the basis ofthe input video signal VD1, the video signal VD2 output from the linememory 1 and the angle signal AN, and outputs the result of thiscalculation as an oblique difference absolute value DD.

[0095] The mixing part 5 outputs the vertical interpolated value IDoutput from the vertical interpolation circuit 2, the oblique average ADoutput from the oblique averaging part 3 or a mixed value thereof as thevalue (hereinafter referred to as an interpolated pixel value) IS of theinterpolated pixel on the basis of the oblique difference absolute valueDD output from the oblique difference absolute value operation part 4.Operations of the mixing part 5 are described later in detail.

[0096] According to this embodiment, the vertical interpolation circuit2 corresponds to the first interpolation means or the firstinterpolation unit, the input terminal 6 receiving the angle signal ANcorresponds to the input means or the input terminal, the obliquedifference absolute value calculation part 4 corresponds to thedifference calculation means or the difference calculation unit, theoblique averaging part 3 corresponds to the second interpolation meansor the second interpolation unit, and the mixing part 5 corresponds tothe interpolated value output means or the interpolated value outputunit.

[0097]FIG. 2 is a model diagram for illustrating the relation betweenthe angle of an image and pixels employed for interpolation.

[0098] Referring to FIG. 2, symbol IL denotes an interpolated scanningline, symbol AL denotes a scanning line located above the interpolatedscanning line IL, and symbol BL denotes a scanning line located underthe interpolated scanning line IL. The upper scanning line AL includespixels A1 to A5, and the lower scanning line BL includes pixels B1 toB5. Symbol IN denotes an interpolated pixel.

[0099] Referring to FIG. 2, the angle of the image is about 45° withrespect to the horizontal line, as shown by arrow d0. In this case, theangle signal AN shown in FIG. 1 indicates the angle of 45°. The obliqueaveraging part 3 shown in FIG. 1 outputs the average of the luminancevalues of the pixels A4 and B2 of the upper and lower scanning lines ALand BL located in the direction of the angle 45° about the interpolatedpixel IN as the oblique average AD. The oblique difference absolutevalue operation part 4 shown in FIG. 1 outputs the absolute value of thedifference between the luminance values of the pixels A4 and B2 of theupper and lower scanning lines AL and BL located in the direction of theangle 45° about the interpolated pixel IN.

[0100]FIG. 3 is a model diagram for illustrating the operations of themixing part 5 shown in FIG. 1.

[0101] As shown in FIG. 3, the mixing part 5 outputs the oblique averageAD output from the oblique averaging part 3 as the interpolated pixelvalue IS when the oblique difference absolute value DD output from theoblique difference absolute value operation part 4 is zero. When theoblique difference absolute value DD output from the oblique differenceabsolute vale operation part 4 is in excess of a previously setthreshold TH, the mixing part 5 outputs the vertical interpolated valueID output from the vertical interpolation circuit 2 as the interpolatedpixel value IS. When the oblique difference absolute value DD outputfrom the oblique difference absolute value operation part 4 is betweenzero and the threshold TH, the mixing part 5 mixes the oblique averageAD output from the oblique averaging part 3 and the verticalinterpolated value ID output from the vertical averaging part 3 witheach other in a ratio responsive to the oblique difference absolutevalue DD, and outputs the mixed value as the interpolated pixel valueIS.

[0102]FIG. 4 is a model diagram showing the relation between the obliquedifference absolute value DD and coefficients K1 and K2 of the verticalinterpolated value ID and the oblique average AD.

[0103] When the oblique difference absolute value DD is between zero andthe threshold TH, the mixing part 5 shown in FIG. 1 calculates the mixedvalue CX as follows:

CX=K1·AD+K2·ID  (1)

[0104] In the above equation (1), K1 and K2 represent the coefficientsof the oblique average and the vertical interpolated value respectively.The coefficients K1 and K2 are so set that K1+K2 regularly reaches 1.Referring to FIG. 4, the horizontal axis shows the oblique differenceabsolute value DD, and the vertical axis shows the coefficients K1 andK2.

[0105] As shown in FIG. 4, the coefficient K1 of the oblique average ADreaches 1.0 when the oblique difference absolute value DD is zero, isreduced as the oblique difference absolute value DD is increased, andreaches zero when the oblique difference absolute value DD is at thethreshold TH. On the other hand, the coefficient K2 of the verticalinterpolated value ID reaches zero when the oblique difference absolutevalue DD is zero, is increased as the oblique difference absolute valueDD is increased, and reaches 1.0 when the oblique difference absolutevalue DD is at the threshold TH.

[0106] While the coefficients K1 and K2 of the oblique average AD andthe vertical interpolated value ID are linearly reduced and increasedwith respect to the oblique difference absolute value DD in the exampleshown in FIG. 4, the present invention is not restricted to this but thecoefficients K1 and K2 of the oblique average AD and the verticalinterpolated value ID may alternatively be changed in a curved manner.

[0107] In the scanning line interpolation equipment according to thisembodiment, the mixing part 5 mixes the vertical interpolated value IDand the oblique average AD with each other while varying the ratiotherebetween in response to the oblique difference absolute value DD andoutputs the mixed value CX as the interpolated pixel value IS when theoblique difference absolute value DD is between zero and the thresholdTH, whereby smooth interpolation is enabled in the image having anoblique edge.

[0108] While the mixing part 5 outputs the oblique average AD as theinterpolated pixel value IS only when the oblique difference absolutevalue DD is zero, the present invention is not restricted to this butthe mixing part 5 may alternatively be set to output the oblique averageAD as the interpolated pixel value IS at an arbitrary value greater thanzero and less than the threshold TH.

[0109] (2) Second Embodiment

[0110]FIG. 5 is a block diagram showing the structure of a scanning lineinterpolation equipment according to a second embodiment of the presentinvention.

[0111] The scanning line interpolation equipment shown in FIG. 5includes a line memory 11, a vertical interpolation circuit 12, avertical upper and lower pixel value extraction part 13, an obliqueaveraging part 14, a vertical upper and lower pixel difference absolutevalue operation part 15, an oblique difference absolute value operationpart 16, a selector 17, a minimum value determination part 18, anotherselector 19, an intermediate value determination part 20 and a mixingpart 21.

[0112] A video signal VD1 is input in the line memory 11, the verticalinterpolation circuit 12, the vertical upper and lower pixel valueextraction part 13, the oblique averaging part 14, the vertical upperand lower pixel difference absolute value operation part 15 and theoblique difference absolute value operation part 16. An angle signal ANis input in the oblique averaging part 14 and the oblique differenceabsolute value operation part 16 through an input terminal 22.

[0113] The line memory 11 delays the input video signal VD1 by one line(one scanning line) and outputs a video signal VD2. The video signal VD2output from the line memory 11 is supplied to the vertical interpolationcircuit 12, the vertical upper and lower pixel value extraction part 13,the oblique averaging part 14, the vertical upper and lower pixeldifference absolute value operation part 15 and the oblique differenceabsolute value operation part 16.

[0114] Also in this embodiment, it is assumed that the video signals VD1and VD2 have luminance of 256 gradations. In other words, the minimumand maximum values of the luminance of the video signals VD1 and VD2 are“0” and “255” respectively.

[0115] Similarly to the vertical interpolation circuit 2 shown in FIG.1, the vertical interpolation circuit 12 vertically interpolates aninterpolated pixel with pixels vertically located above and under thesame on the basis of the input video signal VD1 and the video signal VD2output from the line memory 11 and outputs a vertical interpolated valueID.

[0116] The vertical upper and lower pixel value extraction part 13outputs the values of pixels of upper and lower scanning linesvertically located with respect to the interpolated pixel as a verticalupper pixel value P and a vertical lower pixel value Q respectively onthe basis of the input video signal VD1 and the video signal VD2 outputfrom the line memory 11.

[0117] The oblique averaging part 14 averages the values of pixels ofupper and lower scanning lines located in a direction (hereinafterreferred to as a direction 0) of an angle indicated by the angle signalAN with respect to the interpolated pixel on the basis of the inputvideo signal VD1, the video signal VD2 output from the line memory 11and the angle signal AN, and outputs the result of this calculation asan oblique average Ab. The oblique averaging part 14 further averagesthe values of pixels of upper and lower scanning lines located in adirection (hereinafter referred to as a direction −1) of an angle lessthan the angle indicated by the angle signal AN by 1 and outputs theresult of this calculation as another oblique average Aa, whileaveraging the values of upper and lower scanning lines located in adirection (hereinafter referred to as a direction +1) greater than theangle indicated by the angle signal AN by 1 and outputting the result ofthis calculation as still another oblique average Ac.

[0118] The vertical upper and lower pixel difference absolute valueoperation part 15 calculates the absolute value of the differencebetween the values of the pixels of the upper and lower pixelsvertically located with respect to the interpolated pixel on the basisof the input video signal VD1 and the video signal VD2 output from theline memory 11, and outputs the result as a vertical difference absolutevalue AB.

[0119] The oblique difference absolute value operation part 16calculates the absolute value of the difference between the pixels ofthe values of the upper and lower scanning lines located in thedirection (direction zero) of the angle indicated by the angle signal ANwith respect to the interpolated pixel on the basis of the input videosignal VD1, the video signal VD2 output from the lie memory 11 and theangle signal AN, and outputs the result of this calculation as anoblique difference absolute value Db. The oblique difference absolutevalue operation part 16 further calculates the absolute value of thedifference between the values of the pixels of the upper and lowerscanning lines located in the direction (direction −1) of the angle lessthan the angle indicated by the angle signal AN by 1 and outputs theresult of this calculation as an oblique difference absolute value Da,while calculating the absolute value of the difference between thevalues of the pixels of the upper and lower scanning lines located inthe direction (direction +1) greater than the angle indicated by theangle signal AN by 1 and outputting the result of this calculation as anoblique difference absolute value Dc.

[0120] The minimum value determination part 18 determines the minimumvalue of the oblique difference absolute values Da, Db and Dc outputfrom the oblique difference absolute value operation part 16, andsupplies the result of determination indicating the minimum angle to theselectors 17 and 19.

[0121] On the basis of the result of determination supplied from theminimum value determination part 18, the selector 17 selects the obliqueaverage corresponding to the angle indicated by the result ofdetermination from the oblique averages Aa, Ab and Ac output from theoblique averaging part 14, and outputs the selected average as anoblique average R.

[0122] On the basis of the result of determination supplied from theminimum value determination part 18, the selector 19 selects the obliquedifference absolute value corresponding to the angle indicated by theresult of determination from the oblique difference absolute values Da,Db and Dc output from the oblique difference absolute value operationpart 16, and outputs the selected oblique difference absolute value asan oblique difference absolute value S.

[0123] The intermediate value determination part 20 determinates theintermediate value of the vertical upper and lower pixel values P and Qoutput from the vertical upper and lower pixel value extraction part 13and the oblique average R output from the selector 17, and outputs theresult of determination to the mixing part 21.

[0124] On the basis of the oblique difference absolute value S outputfrom the selector 19, the mixing part 21 outputs the verticalinterpolated value ID output from the vertical interpolation circuit 12,the oblique average R output from the selector 17 or a mixed valuethereof as an interpolated pixel value IS. The mixed value of theoblique difference absolute value S and the vertical interpolated valueID is calculated by a method similar to that for calculating the mixedvalue of the oblique average AD and the vertical interpolated value IDshown in FIGS. 2 and 3.

[0125] When the result of determination of the intermediate valuedetermination 20 is not the oblique average R, i.e. when the obliqueaverage R is not the intermediate value between the vertical upper pixelvalue P and the vertical lower pixel value Q, the mixing part 21 outputsthe vertical interpolated value ID output from the verticalinterpolation circuit 12 as the interpolated pixel value IS. Thus, notoblique interpolation but vertical interpolation is performed when theoblique average R is not between the pixels above and under theinterpolated pixel.

[0126] When the vertical difference absolute value AB supplied from thevertical upper and lower pixel difference absolute value operation part15 is less than a predetermined value, the oblique difference absolutevalue operation part 16 outputs the maximum luminance “255” as theoblique difference absolute values Da, Db and Dc respectively. Thus, theoblique difference absolute value S output from the selector 19 reachesthe maximum value “255”. Therefore, the mixing part 21 outputs thevertical interpolated value ID output from the vertical interpolationcircuit 12 as the interpolated pixel value IS. In other words, notoblique interpolation but vertical interpolation is performed when theabsolute value of the difference between the pixels above and under theinterpolated pixel is small.

[0127] According to this embodiment, the vertical interpolation circuit12 corresponds to the first interpolation means or the firstinterpolation unit, the input terminal 22 receiving the angle signal ANcorresponds to the input means or the input terminal, the obliquedifference absolute value operation part 16 corresponds to thedifference calculation means or the difference calculation unit, theoblique averaging part 14 corresponds to the second interpolation meansor the second interpolation unit, and the mixing part 22 corresponds tothe interpolated value output means or the interpolated value outputunit.

[0128] The minimum value determination part 18 corresponds to theminimum value determination means or the minimum value determinationunit, the selector 17 corresponds to the selection means or theselection unit, the vertical upper and lower pixel value extraction part13 corresponds to the detection means or the detection unit, theintermediate value determination part 20 corresponds to the intermediatevalue determination means or the intermediate value determination unit,and the vertical upper and lower pixel difference absolute valueoperation part 15 corresponds to the vertical difference operation meansor the vertical difference operation unit.

[0129]FIG. 6 is a model diagram for illustrating oblique interpolationby the oblique averaging part 14 and the oblique difference absolutevalue operation part 16 shown in FIG. 5.

[0130] Referring to FIG. 6, symbol IL denotes an interpolated scanningline, symbol AL denotes a scanning line located above the interpolatedscanning line IL, and symbol BL denotes a scanning line located underthe interpolated scanning line IL. The upper scanning line AL includespixels A1 to A5, and the lower scanning line BL includes pixels B1 toB5. Symbol IN denotes an interpolated pixel.

[0131] Referring to FIG. 6, further, arrow d0 shows the angle of theimage indicated by the angle signal AN shown in FIG. 5, arrow d− denotesthe direction −1 and arrow d+ denotes the direction +1.

[0132] The oblique averaging part 14 shown in FIG. 5 outputs the averageluminance of the pixels A4 and B2 of the upper and lower scanning linesAL and BL located along arrow d0 about the interpolated pixel IN as theoblique average Ab, outputs the average luminance of the pixels A5 andB1 of the upper and lower scanning lines AL and BL located along arrowd− as the oblique average Aa, and outputs the average luminance of thepixels A3 and B3 of the upper and lower scanning lies AL and BL locatedalong arrow d+ as the oblique average Ac. The oblique differenceabsolute value operation part 14 shown in FIG. 5 further outputs theabsolute value of the difference between the luminance values of thepixels A4 and B2 of the upper and lower scanning lines AL and BL locatedalong arrow d0 about the interpolated pixel IN as the oblique differenceabsolute value Db, outputs the absolute value of the difference betweenthe luminance values of the pixels A5 and B1 of the upper and lowerscanning lines AL and BL located along arrow d− as the obliquedifference absolute value Da, and outputs the absolute value of thedifference between the luminance values of the pixels A3 a B3 of theupper and lower scanning lines AL and BL located along arrow d+ as theoblique difference absolute value Dc.

[0133] The scanning line interpolation equipment according to thisembodiment mixes the vertical interpolated value ID and the obliquedifference absolute value R with each other while varying the ratiotherebetween in response to the oblique difference absolute value S whenthe oblique difference absolute value S is between zero and a thresholdTH and outputs the result as the interpolated pixel value IS, whereby animage having an oblique edge can be smoothly interpolated.

[0134] Further, the scanning line interpolation circuit determines thedirection having the highest correlation among the direction indicatedby the angle signal AN and the directions −1 and +1 on the basis of theoblique difference absolute values Da, Db and Dc calculated by theoblique difference absolute value operation part 16 and selects theoblique average corresponding to the direction having the highestcorrelation from the oblique averages Aa, Ab and Ac calculated by theoblique averaging part 14, whereby false detection of the angle of theimage can be corrected.

[0135] In the image having an oblique edge, the value of theinterpolated pixel is between the values of the upper and lower pixels.If the oblique average R is not between the values of the pixels locatedabove and under the interpolated pixel, not oblique interpolation butvertical interpolation is so performed that the interpolated pixel valueIS can be prevented from calculation on the basis of pixels located in afalse direction when the angle of the image is falsely detected.

[0136] In the image having an oblique edge, further, the differencebetween the pixels vertically located above and under the interpolatedpixel is large. If the absolute value of the difference between thepixels located above and under the interpolated pixel is small,therefore, not oblique interpolation but vertical interpolation is soperformed that the picture quality can be prevented from deteriorationcaused by false detection of the angle of the image.

[0137]FIG. 7 is a block diagram showing an exemplary structure of theimage angle detector outputting the angle signal AN.

[0138] The image angle detector shown in FIG. 7 includes a line memory31, a binarization part 32, an in-detection window video signalprocessing part 33, a pattern matching angle detection part 34 and areference pattern generation part 35.

[0139] The video signal VD1 is input in the line memory 31, thebinarization part 32 and the in-detection window video signal processingpart 33. The line memory 31 delays the input video signal VD1 by oneline (one scanning line) and outputs the video signal VD2. The videosignal VD2 output from the line memory 31 is supplied to thebinarization part 32 and the in-detection window video signal processingpart 33.

[0140] The binarization part 32 binarizes the input video signal VD1 andthe video signal VD2 output from the line memory 31 with a threshold ofan average luminance value LU supplied from the in-detection windowvideo signal processing part 33 described later, and outputs a binarizedpattern BI formed by “1” and “2”. The binarized pattern BI has the sizeof a detection window.

[0141] The detection window is a rectangular area of 7 by 2 pixelsincluding seven pixels of the video signal VD1 and seven pixels of thevideo signal VD2, a rectangular area of 15 by 2 pixels including 15pixels of the video signal VD1 and 15 pixels of the video signal VD2 orthe like, for example. In the following description, it is assumed thatthe size of the detection window is 7 by 2 pixels. In this case, thesize of the binarized pattern BI corresponds to 7 by 2 pixels.

[0142] The in-detection window video signal processing part 33 sets thedetection window for the input video signal VD1 and the video signal VD2output from the line memory 31 and averages the luminance values of thevideo signals VD1 and VD2 in the detection window for supplying theaverage luminance value LU to the binarization part 32 as the thresholdfor binarization.

[0143] The reference pattern generation part 35 generates a plurality ofreference patterns RA formed by “1” and “0” and supplies the same to thepattern matching angle detection part 34. Each reference pattern RA isequal in size to the detection window.

[0144] The pattern matching angle detection part 34 compares thebinarized pattern BI supplied from the binarization part 32 with each ofthe plurality of reference patterns RA supplied from the referencepattern generation part 35, and outputs the angle of the referencepattern RA matching with the binarized pattern BI as the angle signalAN. The operation of comparing the binarized pattern BI and eachreference pattern RA with each other is hereinafter referred to aspattern matching.

[0145]FIG. 8 is a model diagram showing an exemplary binarized patternBI output from the binarization part 32 shown in FIG. 7.

[0146] Referring to FIG. 8, symbol IN denotes an interpolated pixel, andsymbol IL denotes an interpolated scanning line. Symbols AL and BLdenote scanning lines located above and under the interpolated scanningline IL respectively.

[0147]FIG. 8 shows portions (dark portions) having low luminance with“0”, while showing portions (light portions) having high luminance with“1”. In the binarized pattern BI, the angle of the edge of the image is45°. It is assumed that the horizontal angle is zero and the obliqueupper right angle is positive.

[0148] FIGS. 9(a) to 9(e) are model diagrams showing exemplary referencepatterns generated by the reference pattern generation part 35 shown inFIG. 7. Referring to FIGS. 9(a) to 9(e), halftone-dot squares showpixels of upper and lower scanning lines employed for calculating valuesof interpolated pixels shown by thick lines.

[0149] FIGS. 9(a), 9(b), 9(c), 9(d) and 9(e) show reference patterns of45°, 34°, 27°, 22° and 18° respectively. Referring to FIGS. 9(a) to9(e), upper left portions are dark while lower right portions are light.

[0150] As shown in FIGS. 9(a) to 9(e), not only the angles of straightlines connecting pixels located on point-symmetrical positions about theinterpolated pixel but also angles between these angles can be set inthe reference patterns according to two-dimensional luminancedistribution. For example, the angles 34° and 22° between the angles45°, 27° and 18° can be set.

[0151] For example, the binarized pattern BI shown in FIG. 8 matcheswith the reference pattern shown in FIG. 9(a). In this case, the patternmatching angle detection part 35 shown in FIG. 7 outputs an angle signalAN indicating 45°.

[0152] The image angle detector shown in FIG. 7 can detect the angle ofthe image with a small circuit scale by converting the luminancedistribution of the video signals VD1 and VD2 in the detection window tothe binarized pattern BI and pattern-matching the binarized pattern BIwith the previously set plurality of reference patterns RA.

[0153] In this case, the average luminance value in the detection windowis employed as the threshold for binarization, whereby the binarizedpattern BI can be created regardless of the luminance level of the imagewithout externally setting the threshold for binarization.

[0154] Further, false detection is suppressed as compared with the caseof employing the difference value between two pixels due to the patternmatching according to two-dimensional luminance distribution, wherebythe angle of the image having an oblique edge can be correctly detected.

[0155] When the reference patterns RA according to two-dimensionalluminance distribution are employed, the detected angles are notrestricted to those of straight lines connecting pixels located onpoint-symmetrical positions about the interpolated pixel but anglesbetween these angles can also be detected. Therefore, the angles can bedetected at smaller intervals with the line memory 31 having smallcapacity.

[0156]FIG. 10 is a block diagram showing another exemplary structure ofthe image angle detector outputting the angle signal AN.

[0157] The image angle detector shown in FIG. 10 includes a line memory41, an upper line maximal/minimal detection part 42, a lower linemaximal/minimal detection part 43, a pattern matching angle detectionpart 44 and a reference pattern generation part 45.

[0158] The video signal VD1 is input in the line memory 41 and the lowerline maximal/minimal detection part 43. The line memory 41 delays theinput video signal VD1 by one line (one scanning line) and outputs thevideo signal VD2. The video signal VD2 output from the line memory 41 issupplied to the upper line maximal/minimal detection part 42.

[0159] The upper line maximal/minimal detection part 42 detects themaximal and minimal points of horizontal luminance distribution in thevideo signal VD2 output from the line memory 41 and supplies amaximal/minimal pattern P1 indicating the positions of the maximal andminimal points to the pattern matching angle detection part 44. Thelower line maximal/minimal detection part 43 detects the maximal andminimal points of horizontal luminance distribution in the input videosignal VD1 and supplies a maximal/minimal pattern P2 indicating thepositions of the maximal and minimal points to the pattern matchingangle detection part 44. Each of the maximal/minimal patterns P1 and P2has a size corresponding to one scanning line of a detection window.

[0160] The detection window is a rectangular area of 7 by 2 pixelsincluding seven pixels of the video signal VD1 and seven pixels of thevideo signal VD2, a rectangular area of 15 by 2 pixels including 15pixels of the video signal VD1 and 15 pixels of the video signal VD2 orthe like, for example. In the following description, it is assumed thatthe size of the detection window is 7 by 2 pixels. In this case, thesize of each of the maximal/minimal patterns P1 and P2 corresponds toseven pixels.

[0161] The reference pattern generation part 45 generates a plurality ofreference patterns RB indicating positions of maximal and minimal pointsin the detection window, and supplies the same to the pattern matchingangle detection part 44. Each of the reference patterns RB is equal insize to the detection window.

[0162] The pattern matching angle detection part 44 compares themaximal/minimal pattern P1 output from the upper line maximal/minimaldetection part 42 and the maximal/minimal pattern P2 output from thelower maximal/minimal detection part 43 with each of the plurality ofreference patterns RB supplied from the reference pattern generationpart 45, and outputs the angle signal AN indicating the angle of thereference pattern RB matching with the maximal/minimal patterns P1 andP2.

[0163] The operation of comparing the maximal/minimal patterns P1 and P2with each reference pattern RB is hereinafter referred to as patternmatching.

[0164]FIG. 11 is a model diagram showing exemplary maximal/minimalpatterns P1 and P2 output from the upper line maximal/minimal detectionpart 42 and the lower line maximal/minimal detection part 43 shown inFIG. 10 respectively.

[0165] Referring to FIG. 11, symbol IN denotes an interpolated pixel,and symbol IL denotes an interpolated scanning line. Symbol AL denotes ascanning line located above the interpolated scanning line IL, andsymbol BL denotes a scanning line located under the interpolatedscanning line IL.

[0166]FIG. 11 shows positions of pixels having maximal and minimalpoints in horizontal luminance distribution as “large” and “small”respectively. In practice, the positions of the pixels having themaximal and minimal points are denoted by predetermined numericalvalues. In the maximal/minimal patterns P1 and P2, the angle of straightlines connecting the maximal points with each other and those connectingthe minimal points with each other is 45° in the luminance distributionof the scanning lines AL and BL. It is assumed that the horizontal angleis zero and the oblique upper right angle is positive.

[0167] FIGS. 12(a) and 12(b) are model diagrams showing exemplaryreference patterns generated by the reference pattern generation part 45shown in FIG. 10.

[0168] FIGS. 12(a) and 12(b) show reference patterns of 45° and 34°respectively. These figures show positions of pixels having maximal andminimal points as “large” and “small” respectively. In practice, thepositions of the pixels having the maximal and minimal points areindicated by predetermined numerical values.

[0169] As shown in FIGS. 12(a) and 12(b), angles of straight linesconnecting maximal points and those connecting minimal points are set to45° and 34° respectively in the luminance distribution of the twoscanning lines with reference to pairs of maximal and minimal points.

[0170] For example, the maximal/minimal patterns P1 and P2 shown in FIG.1 match with the reference pattern shown in FIG. 12(a). In this case,the pattern matching angle detection part 44 shown in FIG. 10 outputs anangle signal AN indicating 45°.

[0171] The image angle detector shown in FIG. 10 can detect the angle ofthe image with a small circuit scale by creating the maximal/minimalpatterns P1 and P2 indicating the positions of the maximal and minimalpoints in the luminance distribution of the video signals VD1 and VD2 inthe detection window and pattern-matching the maximal/minimal patternsP1 and P2 with the previously set plurality of reference patterns RB.

[0172] In this case, the angle of an image having thin oblique lines canbe detected by detecting the maximal and minimal points as pairs.

[0173] Further, false detection is suppressed as compared with the caseof employing the difference value between two pixels due to the patternmatching according to two-dimensional luminance distribution, wherebythe angle of the image having small oblique lines can be correctlydetected.

[0174] When the reference patterns RB according to two-dimensionalluminance distribution are employed, the detected angles are notrestricted to those of straight lines connecting pixels located onpoint-symmetrical positions about the interpolated pixel but anglesbetween these angles can also be detected. Therefore, the angles can bedetected at smaller intervals with the line memory 41 having smallcapacity.

[0175] When performing processing with the vertical upper and lowerpixel value extraction part 13 and the intermediate vale determinationpart 20 shown in FIG. 5 and performing processing with the verticalupper and lower pixel difference absolute value operation part 15, it ispreferable to employ the image angle detector shown in FIG. 7.

[0176] The structure of the image angle detector is not restricted tothe above examples but a well-known correlation determination circuitdisclosed in Japanese Patent Laid-Open No. 1-33167 (1989), for example,may alternatively be employed.

[0177] When the difference value between pixels obliquely located withrespect to a pixel to be interpolated is between first and secondvalues, the value of the pixel to be interpolated is calculated by anoperation employing a first interpolated value calculated with verticalpixels and a second interpolated value calculated with the obliquepixels according to the present invention, whereby an image having anoblique edge can be smoothly interpolated.

[0178] Although the present invention has been described and illustratedin detail, it is clearly understood that the same is by way ofillustration and example only and is not to be taken by way oflimitation, the spirit and scope of the present invention being limitedonly by the terms of the appended claims.

What is claimed is:
 1. A scanning line interpolation equipmentinterpolating a scanning line by calculating the value of a pixel to beinterpolated on the basis of an input video signal, comprising: firstinterpolation means calculating a first interpolated value byinterpolation employing pixels of upper and lower scanning linesvertically located with respect to said pixel to be interpolated; inputmeans inputting a signal indicating the direction of an image withrespect to said pixel to be interpolated; difference calculation meanscalculating the difference value between the values of pixels of upperand lower scanning lines located in the direction indicated by saidsignal input by said input means with respect to said pixel to beinterpolated; second interpolation means calculating a secondinterpolated value by interpolation employing said pixels of said upperand lower scanning lines located in the direction indicated by saidsignal input by said input means with respect to said pixel to beinterpolated; and interpolated value output means outputting said secondinterpolated value calculated by said second interpolation means as thevalue of said pixel to be interpolated when the difference valuecalculated by said difference calculation means is not more than a firstvalue, outputting said first interpolated value calculated by said firstinterpolation means as the value of said pixel to be interpolated whenthe difference value calculated by said difference calculation means isnot less than a second value greater than said first value, andcalculating a third interpolated value by an operation employing saidfirst interpolated value calculated by said first interpolation meansand said second interpolated value calculated by said secondinterpolation means and outputting said third interpolated value as thevalue of said pixel to be interpolated when the difference valuecalculated by said difference calculation means is within the rangebetween said first value and said second value.
 2. The scanning lineinterpolation equipment according to claim 1, wherein said interpolatedvalue output means adds said first interpolated value calculated by saidfirst interpolation means and said second interpolated value calculatedby said second interpolation means to each other in a ratio according tothe difference value calculated by said difference calculation meanswhen said difference value is within the range between said first valueand said second value, and outputs the result of addition as the valueof said pixel to be interpolated.
 3. The scanning line interpolationequipment according to claim 2, wherein said interpolated value outputmeans adds said first interpolated value and said second interpolatedvalue to each other so that the ratio of said first interpolated valuecalculated by said first interpolation means is increased and the ratioof said second interpolated value calculated by said secondinterpolation means is reduced as the difference value calculated bysaid difference calculation means approaches said second value from saidfirst value.
 4. The scanning line interpolation equipment according toclaim 1, wherein said difference calculation means calculates thedifference values between the values of a plurality of pixels located ina plurality of directions about the direction indicated by said signalinput by said input means with respect to said pixel to be interpolatedrespectively, and said second interpolation means calculates a pluralityof second interpolated values by interpolation employing said pluralityof pixels located in said plurality of directions about the directionindicated by said signal input by said input means with respect to saidpixel to be interpolated respectively, said scanning line interpolationequipment further comprising: minimum value determination meansdetermining the minimum value among the plurality of difference valuescalculated by said difference calculation means, and selection meansselecting a second interpolated value corresponding to the differencevalue determined as the minimum value by said minimum valuedetermination means from said plurality of second interpolated valuescalculated by said second interpolation means and supplying the selectedsecond interpolated value to said interpolated value output means. 5.The scanning line interpolation equipment according to claim 1, furthercomprising: detection means detecting the values of pixels verticallylocated above and under said pixel to be interpolated respectively, andintermediate value determination means determining whether or not saidsecond interpolated value calculated by said second interpolation meansis between the values detected by said detection means, wherein saidinterpolated value output means outputs said first interpolated valuecalculated by said first interpolation means as the value of said pixelto be interpolated regardless of the difference value calculated by saiddifference calculation means when said intermediate value determinationmeans determines that said second interpolated value is not between thevalues detected by said detection means.
 6. The scanning lineinterpolation equipment according to claim 1, further comprisingvertical difference operation means calculating the difference valuebetween pixels vertically located above and under said pixel to beinterpolated, wherein said interpolated value output means outputs saidfirst interpolated value calculated by said first interpolation meansregardless of the difference value calculated by said differencecalculation means when the difference value calculated by said verticaldifference operation means is less than a predetermined value.
 7. Thescanning line interpolation equipment according to claim 1, wherein saidsecond interpolation means averages said pixels of said upper and lowerscanning lines located in the direction indicated by said signal inputby said input means with respect to said pixel to be interpolated assaid second interpolated value.
 8. The scanning line interpolationequipment according to claim 1, wherein said first value is zero, andsaid second value is a preset threshold.
 9. The scanning lineinterpolation equipment according to claim 1, further comprising imageangle detection means detecting an image angle related to said pixel tobe interpolated on the basis of said input video signal and supplyingsaid signal indicating the direction of said image to said input means,wherein said image angle detection means includes: binarized patterngeneration means binarizing said input video signal in a predetermineddetection area including a plurality of scanning lines and said pixel tobe interpolated and generating a binarized pattern, reference patterngeneration means generating a binary image having a plurality ofdirections as a plurality of reference patterns, and comparison meanscomparing said binarized pattern generated by said binarized patterngeneration means with each of said plurality of reference patternsgenerated by said reference pattern generation means and detecting saidimage angle related to said pixel to be interpolated on the basis of theresult of comparison.
 10. The scanning line interpolation equipmentaccording to claim 1, further comprising image angle detection meansdetecting an image angle related to said pixel to be interpolated on thebasis of said input video signal and supplying said signal indicatingthe direction of said image to said input means, wherein said imageangle detection means includes: maximal/minimal pattern generation meansgenerating a maximal/minimal pattern indicating the position of themaximal point or the minimal point of horizontal luminance distributionevery scanning line in a predetermined detection area including aplurality of scanning lines and said pixel to be interpolated in saidinput video signal, reference pattern generation means generating aplurality of reference patterns indicating the positions of the maximalpoints or the minimal points of horizontal luminance distribution everyscanning line in said detection area, and comparison means comparingsaid maximal/minimal pattern generated by said maximal/minimal patterngeneration means with each of said plurality of reference patternsgenerated by said reference pattern generation means and detecting saidimage angle related to said pixel to be interpolated on the basis of theresult of comparison.
 11. A scanning line interpolation equipmentinterpolating a scanning line by calculating the value of a pixel to beinterpolated on the basis of an input video signal, comprising: a firstinterpolation device that calculates a first interpolated value byinterpolation employing pixels of upper and lower scanning linesvertically located with respect to said pixel to be interpolated; aninput terminal that receives a signal indicating the direction of animage with respect to said pixel to be interpolated; a differencecalculation device that calculates the difference value between thevalues of pixels of upper and lower scanning lines located in thedirection indicated by said signal received in said input terminal withrespect to said pixel to be interpolated; a second interpolation devicethat calculates a second interpolated value by interpolation employingsaid pixels of said upper and lower scanning lines located in thedirection indicated by said signal received in said input terminal withrespect to said pixel to be interpolated; and an interpolated valueoutput device that outputs said second interpolated value calculated bysaid second interpolation device as the value of said pixel to beinterpolated when the difference value calculated by said differencecalculation device is not more than a first value, outputs said firstinterpolated value calculated by said first interpolation device as thevalue of said pixel to be interpolated when the difference valuecalculated by said difference calculation device is not less than asecond value greater than said first value, and calculates a thirdinterpolated value by an operation employing said first interpolatedvalue calculated by said first interpolation device and said secondinterpolated value calculated by said second interpolation device andoutputs said third interpolated value as the value of said pixel to beinterpolated when the difference value calculated value by saiddifference calculation device is within the range between said firstvalue and said second value.
 12. The scanning line interpolationequipment according to claim 11, wherein said interpolated value outputdevice adds said first interpolated value calculated by said firstinterpolation device and said second interpolated value calculated bysaid second interpolation device to each other in a ratio according tothe difference value calculated by said difference calculation devicewhen said difference value is within the range between said first valueand said second value, and outputs the result of addition as the valueof said pixel to be interpolated.
 13. The scanning line interpolationequipment according to claim 12, wherein said interpolated value outputdevice adds said first interpolated value and said second interpolatedvalue to each other so that the ratio of said first interpolated valuecalculated by said first interpolation device is increased and the ratioof said second interpolated value calculated by said secondinterpolation device is reduced as the difference value calculated bysaid difference value calculation device approaches said second valuefrom said first value.
 14. The scanning line interpolation equipmentaccording to claim 11, wherein said difference calculation devicecalculates the difference values between the values of a plurality ofpixels located in a plurality of directions about the directionindicated by said signal received in said input terminal with respect tosaid pixel to be interpolated respectively, and said secondinterpolation device calculates a plurality of second interpolatedvalues by interpolation employing said plurality of pixels located insaid plurality of directions about the direction indicated by saidsignal received in said input terminal with respect to said pixel to beinterpolated respectively, said scanning line interpolation equipmentfurther comprising: a minimum value determination device that determinesthe minimum value among the plurality of difference values calculated bysaid difference calculation device, and a selection device that selectsa second interpolated value corresponding to the difference valuedetermined as the minimum value by said minimum value determinationdevice from said plurality of second interpolated values calculated bysaid second interpolation device and supplies the selected secondinterpolated value to said interpolated value output device.
 15. Thescanning line interpolation equipment according to claim 11, furthercomprising: a detection device that detects the values of pixelsvertically located above and under said pixel to be interpolatedrespectively, and an intermediate value determination device thatdetermines whether or not said second interpolated value calculated bysaid second interpolation device is between the values detected by saiddetection device, wherein said interpolated value output device outputssaid first interpolated value calculated by said first interpolationdevice as the value of said pixel to be interpolated regardless of thedifference value calculated by said difference calculation device whensaid intermediate value determination device determines that said secondinterpolated value is not between the values detected by said detectiondevice.
 16. The scanning line interpolation equipment according to claim11, further comprising a vertical difference operation device thatcalculates the difference value between pixels vertically located aboveand under said pixel to be interpolated, wherein said interpolated valueoutput device outputs said first interpolated value calculated by saidfirst interpolation device regardless of the difference value calculatedby said difference calculation device when the difference valuecalculated by said vertical difference operation device is less than apredetermined value.
 17. The scanning line interpolation equipmentaccording to claim 11, wherein said second interpolation device averagessaid pixels of said upper and lower scanning lines located in thedirection indicated by said signal received in said input terminal withrespect to said pixel to be interpolated as said second interpolatedvalue.
 18. The scanning line interpolation equipment according to claim11, wherein said first value is zero, and said second value is a presetthreshold.
 19. The scanning line interpolation equipment according toclaim 11, further comprising an image angle detection device thatdetects an image angle related to said pixel to be interpolated on thebasis of said input video signal and supplies said signal indicating thedirection of said image to said input terminal, wherein said image angledetection device includes: a binarized pattern generation device thatbinarizes said input video signal in a predetermined detection areaincluding a plurality of scanning lines and said pixel to beinterpolates and generates a binarized pattern, a reference patterngeneration device that generates a binary image having a plurality ofdirections as a plurality of reference patterns, and a comparison devicethat compares said binarized pattern generated by said binarized patterngeneration device with each of said plurality of reference patternsgenerated by said reference pattern generation device and detects saidimage angle related to said pixel to be interpolated on the basis of theresult of comparison.
 20. The scanning line interpolation equipmentaccording to claim 11, further comprising an image angle detectiondevice that detects an image angle related to said pixel to beinterpolated on the basis of said input video signal and supplies saidsignal indicating the direction of said image to said input terminal,wherein said image angle detection device includes: a maximal/minimalpattern generation device that generates a maximal/minimal patternindicating the position of the maximal point or the minimal point ofhorizontal luminance distribution every scanning line in a predetermineddetection area including a plurality of scanning lines and said pixel tobe interpolated in said input video signal, a reference patterngeneration device that generates a plurality of reference patternsindicating the positions of the maximal points or the minimal points ofhorizontal luminance distribution every scanning line in said detectionarea, and a comparison device that compares said maximal/minimal patterngenerated by said maximal/minimal pattern generation device with each ofsaid plurality of reference patterns generated by said reference patterngeneration device and detects said image angle related to said pixel tobe interpolated on the basis of the result of comparison.